Today's vehicle air conditioning system is comprised of the compressor which is engine driven or driven by other means such as an electric motor, an evaporator and a condenser which are all connected together in an operative relationship within the system. Refrigerant flow control means are provided between the condenser and evaporator. With a fixed capillary or orifice or orifice tube refrigerant flow control an accumulator is usually provided between the evaporator and compressor so that the system will be effective under variable vehicle speed and load conditions.
The accumulator of the prior art stores and releases refrigerant into the rest of the system as required since a fixed restriction system requires a specific charge at each operating condition. The accumulator also separates the liquid from the gas refrigerant. It also provides refrigerant charge tolerance for ease of production and provides a reserve in case of future small leakage of refrigerant which is prevalent in today's vehicle systems.
In current designs or prior art devices, fixed restrictor vehicle air conditioning systems incorporate an "oil bleed hole" in the "U" tube of the suction accumulator which returns oil and liquid refrigerant to the compressor. A typical "U" tube construction is shown in U.S. Pat. No. 3,084,523, which issued to E. W. Bottum et al. on Apr. 9, 1963. The amount of liquid return in larger part determines the amount of evaporator "flooding" and the speed at which additional refrigerant is introduced into the operating system when conditions require more charge. The drawbacks of this liquid return to the compressor include a reduction in compressor capacity as compared to only gas being returned to the compressor, increased power consumption and a possibility of compressor damage due to oil dilution and "liquid slugging" especially on start-up when the accumulator "U" tube can be significantly filled. Also pressure drop and cost are disadvantages of the "U" tube design.
Simple elimination of the liquid return would result in oil being trapped in the accumulator and a slow response to additional refrigerant requirements as loads and capacities are varied since the additional refrigerant required would have to be evaporated from the accumulator.